Tag Archives: acre feet

Teton Dam Failure. Actual Data for American Falls.

If you’ve been reading my blog for any length of time, you know I like sources. And moreso, I like hard facts…

A while back I posted a story about Teton Dam and made several comments about American Falls Dam. These comments were based on other websites, the sites did not agree so I had to accept standard deviation. Wanting to have all the facts correct I sent in a request to the Bureau of Reclamation.

This morning I recieved the actual numbers in a very detailed response, Thanks goes to The Burley Office of the Bureau of Reclamation.

Thank you for your interest in getting correct information on American Falls Dam.

Reclamation’s first dam at American Falls was completed in 1927 with a capacity of 1,700,000 acre-feet at a normal maximum water surface of 4354.5 feet. Idaho Power Company had a smaller dam, just downstream, to divert water through their turbines before that time.

By 1973 the concrete of the dam was deteriorating from a chemical reaction between alkaline aggregate and the cement used in the original construction. At that time the capacity of the reservoir was restricted to 1,200,000 acre-feet. At 12:00 a.m., June 5, 1976, the reservoir held 1,145,060 acre-feet.

The following table shows the recorded flows and contents for the first 10 days of June in 1976. Hopefully our e-mail systems will allow the table to remain intact. Inflow and discharge are daily averages and content is the end of day, midnight, observation.

Date    Inflow       Discharge     Content
.         cfs         cfs        acre-feet
1-Jun    17,695      23,700      1,205,800
2-Jun    15,878      22,700      1,192,270
3-Jun    12,775      21,800      1,174,370
4-Jun    12,460      19,700      1,160,010
5-Jun    11,562      19,100      1,145,060
6-Jun    15,810      20,000      1,136,750
7-Jun    37,195      20,200      1,170,460
8-Jun    40,861      21,300      1,209,260
9-Jun    22,288      21,900      1,210,030
10-Jun   16,965      21,800      1,200,440

As you can see, the reservoir was full to restricted capacity, plus a little, on June 1 and began to draft. Inflow and discharge were decreasing. On June 6 discharge was increased slightly and that slight increased persisted until the reservoir returned to full.

The maximum content on June 9 resulted in a water surface elevation just .2 feet above the restricted level.

Reconstruction, completed in 1978, restored the capacity to the original water surface elevation of 4354.5 feet. In 1977, while the reservoir was drained, a new survey of the reservoir area was made.

Subsequently, the capacity of the reservoir was adjusted to 1,672,590 acre-feet. This is a small adjustment considering that more than 50 years passed between surveys.

So, contrary to what alot of other sites were saying, no they did not “drain” the lake. Intake had been decreasing till the event so discharge had been decreasing too, to 19,100 cfs before the event. Post event they increased the discharge, but since intake had been droping, they didn’t increase it much. Actual capacity was 1.2 million acre feet, the inital post-event discharge was maintained while and the lake dropped to 1.13 million acre feet before water arrived. Accroding to the data the water started arriving on the 7th with an AVERAGE DAILY INTAKE of 37,195cfs. I can only assume that for part of of the day, the intake was around normal (pre-event) and a rather large inital surge of water was well over 37,000. I did some checking and found the following data from the same 10 day period taken at a gauge on the river near Blackfoot, ID.

click to view

It shows very similar number to what was provided me in the email response. Though the gauge is upstream so the peaks and averages are going to be earlier than at the dam. This still gives us an average. I was hoping to find an instantaneous reading that would tell us what the inital surge (if any) was. I found the following data from the same gauge.

peak flow
click to view

This graph represents the peak flows for recorded years. Notice that 1976 is the highest year but has a couple of close years too. Not sure the story behind those years. But the corresponding data point for 76 indicates “June 7th 1976 Gague Height 15.44 feet – 53,500cfs (dam failure).”

It would seem we’ve found what I was looking for. Inital surge would have been near 54,000cfs averaging to 37,000cfs intake for the dam for that day.

The dam did fluctuate over capacity slightly as the discharge was changed to reflect the intake. Looks like by the 10th intake, discharge and contents had stabilized to about normal.

Thanks again to the Bureau of Reclamation, Burley office for the American Falls dam history and data. It really clears up descrepancies on other sites and news reports.



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Teton Dam Disaster: June 5, 1976

Teton Dam Rupture

The hole in the Teton Dam grows

June 5th, 2006; the 30 year anniversary of the Teton Dam Break.
UPDATED: This page has been updated to remove some erroneous facts sourced from other webpages. The data I obtained from the Bureau of Reclamation can be found here

The Teton Dam was built on the Teton River upstream from Rexburg, Idaho. at 11:57 am on June 5, 1976 the dam broke, the resulting flood killed 14 people and some estimates put the damage done by the colapse of the 100 million dollar dam, at one billion dollars. Actual federal approved claims totalled almost 400 million dollars. I know a few people who lived there at the time, the stories are incredible.

This is an amazing picture, it was taken by Eunice Olson as the dam broke. Her other shots are an entire sequence of the dam breaking. An arial shot of the break. Here are some great pictures of the flood damage. The next photo was taken sometime after the waters reached the town of Rexburg, photographer unknown.

Rexburg, Idaho after Teton Dam Breach

Rexburg Flood Water

I won’t post copies of all the accounts of the breach (links to those at the bottom) but the initial response of the Sheriff and others was very much disbelief. I have to say I probably wouldn’t have believed it at first either. The next day, the operators of American Falls Dam prepared for the incresed intake. It took almost two days for the 300,000 acre feet of water to reach American Falls. The American Falls Dam wasn’t in the best condition, and was in the process of being replaced. The old dam could hold about 1.2 million acre-feet the replacement dam was being constructed just downstream from the old one but wasn’t done yet. The water released was almost a quater of the capacity of American Falls, obviously it didn’t reach there all at the same time. Here is the data I recieved from the Bureau of Reclamation concerning American Falls at the time of the Teton Failure

A committe was formed in the late 80s to consider rebuilding the dam. To this day, the remains of the Dam are pretty much unchanged aside from

Google Image Search: Teton Dam

Bureau of Reclamation: Teton Dam

Other Sources:
Teton Dam Failure
Teton Dam – Wikipedia


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